The term high-tension as used in conjunction with the invention is to be understood broadly and relates to voltages exceeding 1,000 volts, it including in addition to the high-voltage range in a narrow sense also the medium-voltage range.
High-tension composite insulators are multifunctional components mainly serving electrical insulation as regards leakage distance, dielectric strength and arc withstanding capacity. From a mechanical point of view they handle tensile and compressive stresses, bending whilst also providing mounting functions, for example, as hollow insulators for switches.
Known from prior art are high-tension insulators made of ceramics, cast resin and composite materials, it being the latter that are gaining increasing acceptance. These comprise typically a composite of a glass-fiber reinforced cylindrical rod (solid body) or tube (hollow body) centrally and a shield layer of synthetic material, particularly silicone rubber. As a rule the shield layer itself is made up in turn of an envelope covering the solid or hollow body with weathersheds protruding therefrom like scales and serving to divert away rain and lengthen the so-called leakage distance, i.e. the shortest distance for the leakage current between the two ends of the rod or tube. Secured to the solid or hollow body are end fittings specific to the application concerned. The combination of a solid or hollow body and a synthetic material envelope is simple termed “core” in the following.
Composite insulators including shield layers of a synthetic material, particularly silicone, are given preference mainly for two reasons. Firstly the shield layer of a synthetic material, particularly silicone, is hydrophobic, i.e. the insulators employed mostly outdoors are highly water repellant which is conducive to repelling dirt and thus to low leakage current losses. Secondly, this is a lightweight structure which facilitates assembly.
In practice, a basic distinction is made between two methods of producing composite insulators:                a) the so-called single-molded envelope (see FIG. 1). In this method the shield layer and the weathersheds (the envelope) 2 are molded in a single operation on a solid or hollow body 1 in a mold split lengthwise. The disadvantage here is the the lack of flexibility in producing differing insulator shapes. Apart from this, no undercuts such as grooves on the weathersheds, for instance, can be molded unless multipart molds are used which, however, add considerably to the production costs;        b) a multistage production method (see FIG. 2) in which a shield layer 6 is applied to the solid or hollow body by molding or extrusion whilst the weathersheds 3 are prefabricated separately as a rule by injection and/or compression molding to then be mounted over the core and secured thereto by an adhesive.        
Whilst method b) permits substantially more flexible production than method a) it is still not considered as being an optimum. The bonding joints 4 between weathershed and core have a history of being electrical erosion problem locations, likewise any remaining adhesive film 4a on the core between the weathersheds. Another factor lacking economy is the need to apply the adhesive in special procedures and for the aforementioned electrical reasons to carefully remove excess deposits after siting the weathersheds by tedious manual cleaning.
The object of the invention is accordingly to provide a flexible process of producing high-tension composite insulators which avoids the need to adhesively bond shield layer and weathersheds, this also involving providing a corresponding product, a corresponding material as well as a method in general.